Estrogen lowers breast cancer risk in some women

"Estrogen on its own appears to be safe," said Dr. Anthony Howell, professor of medical oncology at the University of Manchester, who co-authored a commentary in journal.

Scientists aren't sure why estrogen appeared to lower the risk of breast cancer, but Howell said altering the amount of estrogen in the body might help stop tumor growth, since fluctuating levels could interfere with tumor development.

Other experts weren't convinced. "It's inconsistent with the totality of evidence that finds estrogen increases breast cancer risk," said Valerie Beral, director of the cancer epidemiology unit at Oxford University. She said the analysis was a subset of a larger trial that wasn't designed to specifically look at breast cancer.

"If you want to take hormone replacement therapy, estrogen-only has a much lesser effect on breast cancer than with progestin," she said. "But to say it protects against breast cancer is wrong."

Dr. Peter Bowen-Simpkins, medical director of the London Women's Clinic and a spokesman for Britain's Royal College of Obstetricians and Gynaecologists, said the study was still reassuring news for women who had hysterectomies seeking relief from menopausal symptoms.